Plastic bags have become a necessary fixture of retail trade. A significant portion of merchandise is packaged in plastic bags before being delivered to retail operations or before being delivered to customers. A variety of products which are directly delivered to consumer homes, such as newspapers and magazines, are also packaged in plastic bags in order to protect the contents from rain and snow. Also, when consumers purchase items at retail stores, the check-out staff often place the purchased items in plastic bags which often have printed thereon designs such as the retail store's trademarks. These trademarks and designs can help to identify the source of the purchased items and color images and designs can improve the appearance of the bag. The plastic bag that can be used for many of these packaging tasks generally consist of a tubular plastic bag or envelope having a closed end and an opposite opened end. The article is placed in the bag or envelope through the open end and then the bag or envelope can be closed by a variety of means. The term “bag” as used herein is used in its broadest sense (unless the context indicates the contrary) and is meant to include such common bag-like items such as envelopes and pouches.
Variety of devices have been developed for closing the open end of a bag or envelope. For example, twist ties, draw strings and draw tape have been widely employed to close the open end of a bag. Other known closing methods used for bags and/or envelopes include lock-tops, Velcro strips, flip top flaps, moisture activated adhesive strips, pressure sensitive adhesive strips and heat seal closures. Also, it is well known to construct plastic bags with built-in “zipper like” self-closing features which are provided adjacent the open end of the bag and can aid in sealing the bag shut. For example, ZIPLOC® plastic bags have a formed zipper like track formed on the inside of the film surface. It is also known to provide plastic bags which incorporate an adhesive strip that can be used to seal the open end of the bag.
U.S. Pat. No. 3,990,627 which issued Nov. 9, 1976 to Mobile Oil Corporation describes an adhesive closure for a bag such as a sandwich bag. An adhesive strip is located adjacent the open mouth portion of the bag and is covered until ready for use by the upper portion of the bag's front wall. Upward displacement of this upper portion of the front wall exposes the adhesive strip so that it can be used for sealing purposes. The flap section which covers the adhesive strip prior to its use is provided with a strip of release material that is placed in contact with and covers the adhesive strip.
More recent U.S. Pat. No. 4,410,130, which also issued to Mobile Oil Corporation, describes other forms of Z-fold closures for thermo-plastic bags. These closures also employ pressure sensitive adhesive strips as well as a protective strip having one or more ribs so that the strip of adhesive is substantially contacted by only the top portions of the ribs when the bag closure is in the Z-fold position. The protective strips can be made from polyethylene.
While such previously used plastic bags with closure devices have been used with some success for a number of years, there is still a need for an improved sealable bag which can be used quickly and easily and which can be manufactured at a relatively low cost.
Accordingly, it is an object of the present invention to provide an improved bag which includes an adhesive strip for closing an open mouth portion of the bag and a protective band which can extend over and protect the adhesive strip until the bag is ready to be used, this bag also being producible at a reasonably low cost.
It is a further object of the present invention to provide a bag, and in particular a plastic bag, which includes a closure device in the form of an adhesive strip covered by a protective coating, the latter being made by an aqueous coating of release material applied directly to the plastic sheeting using a printing press or coating machine, this coating having been dried and formed prior to forming the bag from the plastic sheeting.
It is a further object of the present invention to provide an improved and inexpensive method of making modified plastic sheeting suitable for manufacturing sealable bags, each provided with a band of release material.